METHOD FOR ACTIVATING AN INNER SURFACE OF A HOLLOW GLASS SUBSTRATE TUBE FOR THE MANUFACTURING OF AN OPTICAL FIBER PREFORM.

摘要

The present invention relates to a method for activating an inner surface of a hollow glass substrate tube for the manufacturing of an optical fiber preform, said method comprising the steps of: i) depositing a number of activation glass layers on said inner surface of said hollow substrate tube by means of a PCVD process wherein the thickness of the activation glass layers is at least 10 micrometer and at most 250 micrometer; and ii) at least partially removing said activation layers deposited in step i) by means of an etching process wherein the activation glass layers as deposited in step i) are removed to an extent of at least 30 %. The present method of by carrying out the etching step on PCVD deposited layers instead of on the initial substrate tube itself the benefits of the etching process - such as the improved adhesion - is retained whereas the negative side effects of the etching - the creation of surface inhomogeneity - is diminished or even fully eliminated.